Reproductive traits of Holsteins and Jerseys. Effects of age, milk yield, and clinical abnormalities on involution of cervix and uterus, ovulation, estrous cycles, detection of estrus, conception rate, and days open.

Milk samples were collected twice weekly from 535 dairy cows between parturition and the re-establishment of pregnancy to monitor ovarian activity by measurement of milk progesterone levels by radioimmunoassay. The mean progesterone levels after fertile and non-fertile first inseminations were similar from 21 days before until 13 days after insemination, those in non-pregnant animals declined while those in pregnant animals continued to rise until Day 22. Progesterone profiles of 47 repeat breeder cows (i.e. receiving greater than 3 inseminations) demonstrated that a variety of patterns was associated with the poor conception rate. A study of the post-partum interval showed that cows resumed cycles by 24 +/- 0.6 days after calving; the length of this interval varied significantly with the season of calving and non-significantly with the lactation number (i.e. age) of the cow, but was not related to yield. Of the 535 cows studied, 5.2% had not started to cycle within 50 days of calving and a further 5.2% resumed cycles which subsequently ceased. The progesterone profiles of acyclic cows indicated that after treatment with 0.5 mg LH-RH or a progesterone-releasing intravaginal device (PRID) for 14 days 75% of animals apparently ovulated but the calving to conception interval was not significantly altered compared with that of untreated control cows.

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Milk progesterone levels in relation to conception, repeat breeding and factors influencing acyclicity in dairy cows

Physiological classification of anovulatory conditions in cattle

Treatment with GnRH and PGF2 alpha is a practical method for controlling ovarian follicular and luteal functions and increasing the precision of estrus synchronization in cyclic and acyclic postpartum cows and heifers. This method reduces considerably the period of time needed for estrus detection; it synchronizes the estrous cycle of 70 to 80% of the cyclic cows to within a 4-d interval without any detrimental effect on the fertility rate (65 to 85%). Moreover, resumption of ovarian activity and normal fertility in acyclic cows in favored. Administration of GnRH eliminates the large follicles by ovulation or atresia and induces emergence of a new follicular wave within 3 to 4 d after treatment at any stage of the estrous cycle, but it limits further growth of these emerging follicles by increasing atresia. The precision of estrus and the unaltered fertility rate is due to the synchronized selection of a new larger growing follicle, which becomes the ovulatory follicle after PGF(2 alpha)-induced luteolysis 6 d after GnRH treatment. Also, fixed-time AI programs without the need for estrus detection may be possible using a second injection of GnRH in a GnRH-PGF(2 alpha)-GnRH protocol to ovulate the selected follicle at a precise time. We describe a physiological model to explain how the precision of estrus is improved following PGF(2 alpha)-induced luteolysis, via the effect of pretreatment with GnRH on follicular development and luteal functions in cattle. Application of this model to the development of reliable methods of fixed-time insemination is also explored.

Synchronization of ovarian follicular waves with a gonadotropin-releasing hormone agonist to increase the precision of estrus in cattle: a review.

Ovarian Follicular Cysts in Dairy Cows

Forty-eight Holstein and Guernsey cows were assigned according to age and breed to one of seven groups based on days following parturition. Cows in Groups II to VII received an intramuscular injection of 100 ~tg gonadotropin releasing hormone (GnRH) on either 1 or 2, 3 or 4, 5 or 6, 7 or 8, 12 or 13, or 18 or 19 days postpartum, respectively (six cows per group). An injection of the carrier vehicle for GnRH was given to cows in Group I (controls), which included two cows per each postpar tum treatment period (12 cows). Prior to treatment, plasma LH increased (P<.05) from a mean concentration of 1.1 + .1 ng/ml at 1 or 2 days postpar tum to 3.5 -+ .6 ng/ml at 18 or 19 days postpartum. Preinjection estradi01-17/3 concentrations tended to increase with days postpar tum (r = .31; P<.07), however, plasma progesterone did not change during the postpar tum interval studied. Following treatment, plasma LH did not increase (P>.05) for cows in Groups I, II, III and IV but was significantly increased in cows of Groups V, VI and VII (P<.05). Peak LH concentrations following GnRH were higher (P<.05) for cows in Groups V to VII (14.1 + 2.7, 11.2 + 2.1 and 13.6 + 2.3 ng/ml, respectively) than those in Groups II to IV (3.1 +1.4, 2.8 + .8 and 4.2 + .6 ng/ml, respectively).

Effect of days postpartum and endogenous reproductive hormones on GNRH-induced LH release in dairy cows.

A study was undertaken to observe hormonal and clinical responses of 24 cows assigned to 1 of 4 dosage groups with ovarian cysts to a single IM injection of 0 50 100 or 250 mcg of synthetic gonadotropin-releasing hormone (GnRH). 16 normally cycling lactating cows were used as the control group. Of the 18 cows receiving GnRH 13 (72%) responded to treatment and returned to estrus 9-26 days following treatment compared with 1-6 receiving 0 mcg GnRH. Increasing firmness of the cystic structures subsequently feeling like corpora lutea was noticed in most cases. A significant increase of plasma luteinizing hormone (LH) was noticed on Day 0 in cows following injection of GnRH. Difference in plasma LH on Day 0 between responders and nonresponders to treatment were insignificant. Plasma progesterone and estradiol concentrations on Day 0 were higher (p less than .01) for responding cows than for nonresponders. Lower LH concentrations were found among responders than among nonresponders on Posttreatment Days 1-13; progeste rone and estradiol concentrations were higher (p less than .05). Mean plasma LH and progesterone concentrations among responders on these days were the same as postestrous concentrations or as mean LH and progesterone concentrations in controls during the postestrous period. Mean plasma estradiol concentrations of cows with ovarian cysts were higher (p less than .005) on the injection day (Day 0) and on Days 1-13 posttreatment than during the subsequent estrous cycle or in postestrous controls. Results of this study indicate that cows with ovarian cysts are capable of releasing LH in response to GnRH.

Hormonal responses of dairy cows with ovarian cysts to GnRH.

Clinical response of dairy cows with ovarian cysts to GnRH.

The objective was to determine the relationship of prior follicular development to GnRH-induced cyclic ovarian activity in dairy cows postpartum. Sixty lactating Holstein and Guernsey cows from the University of Missouri dairy herds were assigned at random to one of two groups. Group I consisted of 20 cows (control) given a single intramuscular (IM) injection of saline. Group II consisted of 40 cows given a single injection of 100 micrograms gonadotropin releasing hormone (GnRH) IM. Treatments were administered 12 to 14 days postpartum. All cows were palpated per rectum to monitor ovarian activity prior to treatment (time 0) and 2 to 3 and 7 to 9 days post-treatment. Blood was collected via tail vessel puncture at time 0 and 7 to 9 days post-treatment. The percentage of cows exhibiting a follicle 10 mm or greater in diameter prior to treatment was not different between Group I (50%) and Group II (43%). However, twenty (50%) of the GnRH-treated cows initiated cyclic ovarian activity following treatment as evidenced by palpable CL and plasma progesterone greater than or equal to 1.0 ng/ml on day 9 post-treatment in contrast to only four (20%) saline-treated cows (P less than 0.05). Seventeen of 20 cows ovulating in Group II exhibited a palpable follicle greater than or equal to 10 mm in diameter prior to treatment compared to 3 of 4 cows in Group I. Prior to treatment, plasma concentrations of LH, estradiol-17 beta and progesterone were not different (P less than .05) between cows in Groups I and II. In Group II, preinjection levels of estradiol-17 beta and LH for cows ovulating in response to GnRH were higher (P less than .01) than in cows not ovulating. Postinjection concentrations of progesterone in plasma on days 7 to 9 were higher (P less than .01) in cows ovulating than in cows not ovulating. Six (30%) cows in Group I developed ovarian cysts prior to conception as compared to 12.5% (5) of the cows in Group II (P less than .05). The present study suggests: (1) GnRH treatment as early as 12 to 14 days postpartum may initiate cyclic ovarian activity in normal dairy cows; (2) elevated preinjection concentrations of estradiol-17 beta and follicular growth are important for GnRH induced ovulations; and (3) GnRH treatment 12 to 14 days postpartum may be useful in reducing abnormal ovarian activity.

Effect of ovarian activity and endogenous reproductive hormones on GnRH-induced ovarian cycles in postpartum dairy cows.

In a study involving 7,477 pregnant cows (5,426 Holstein-Friesians and 2,051 Guernseys), each pregnancy was diagnosed by rectal palpation, using the membrane slip technique. Each cow was examined twice, first by a veterinary student, then by a clinician. Of the cows diagnosed pregnant, 7,058 (94.4%) calved. The embryonic death rate in cows examined during the first 50 days of gestation was significantly (P less than 0.001) greater than that associated with examinations after 50 days of gestation. A significant difference was found between herds in different years (P less than 0.05). There was no conclusive indication that embryonic loss at the time of or shortly after early examination was iatrogenic abortion resulting from the membrane slip technique.

C.J. Bierschwal

Papers

Effect of days postpartum and endogenous reproductive hormones on GNRH-induced LH release in dairy cows.

Hormonal responses of dairy cows with ovarian cysts to GnRH.

Clinical response of dairy cows with ovarian cysts to GnRH.

Effect of ovarian activity and endogenous reproductive hormones on GnRH-induced ovarian cycles in postpartum dairy cows.

Correlation between pregnancy diagnosis by membrane slip and embryonic mortality.